1. Field of the Invention
The present invention relates to a malfunction diagnosis system for an electric vehicle on-board device that includes a malfunction diagnosis section that diagnoses whether the electric vehicle on-board device has a malfunction when supplied with electric power from at least one of an electric storage section or an external power source, and a malfunction diagnosis method therefor.
2. Description of the Related Art
In general, it is contemplated diagnosing whether a malfunction has occurred in a device mounted on an electric vehicle equipped with a traction motor, such as an electric car or a hybrid vehicle, is performed after the ignition switch has been turned off. One example of such a device is mounted on a hybrid vehicle in which drive wheels are driven using at least one of an engine and a motor as a driving source, is an evaporative emission control device that prevents emission of evaporation gas, such as fuel vapor. The function of an evaporative emission control device is to prevent emission of fuel vapor from a fuel tank or the like into the atmosphere, and one typical example of such an evaporative emission control device is a charcoal canister, which has a canister containing activated carbon to adsorb evaporation gas (fuel vapor) from the fuel tank or the like, and an exhaust pipe connected to an intake pipe and the canister so that the fuel vapor is drawn from the canister into the intake pipe by negative pressure in the intake pipe created by intake air, and the fuel vapor is burned in the cylinders of the engine when the engine is operating.
When such an evaporative emission control device is used, the diagnosis of whether a malfunction has occurred, such as a hole that may lead to gas leakage from the pipe connecting the fuel tank and the canister and the exhaust pipe, may be performed with a diagnosis device when the engine is stopped after the ignition switch has been turned off. In this case, to diagnose whether there is a malfunction after the ignition switch has been turned off, the electric power necessary to perform the diagnosis may be supplied to the diagnosis device from a low-voltage secondary battery for auxiliary devices.
Japanese Patent Application Publication No. 2004-266937 (JP-A-2004-266937) describes a battery control device that periodically performs self-diagnosis on an auxiliary secondary battery when the ignition key is turned off, and the device has a microprocessor for diagnosing whether a malfunction has occurred in the auxiliary secondary battery. The malfunction self-diagnosis is performed only once if the result of malfunction diagnosis is the same as the previous result and the determination for self-diagnosis is performed a plurality of times if the result of malfunction diagnosis differs from the previous result. It is described that, with this configuration, the determination for self-diagnosis is performed only once to reduce the current consumption if the result of malfunction detection is the same as the previous result.
If malfunction diagnosis is performed on the evaporative emission control device in an electric vehicle when the vehicle is not driven as described above, the diagnosis device is supplied with electric power from a low-voltage secondary battery for auxiliary devices but the electric power which can be used to operate the diagnosis device is limited because the low-voltage secondary battery is not charged from a power generator. Thus, if malfunction diagnosis is made frequently or for prolonged periods when the diagnosis device is used, the amount of charge in the secondary battery may be excessively decreased, that is, a dead battery may occur. On the other hand, for higher accuracy of malfunction diagnosis, it is preferred that the malfunction diagnosis is made frequently or for prolonged periods.
In recent years, when an electric vehicle is a hybrid vehicle, what is called a “plug-in hybrid vehicle” is contemplated which has a connection unit connectable to an external commercial power source so that a low-voltage secondary battery or a high-voltage secondary battery as a power source for a traction motor may be charged from the commercial power source while the vehicle is not driven. In such a plug-in vehicle, the amount of charge in the low-voltage secondary battery does not become too low when it is charged from an external commercial power source, and the diagnosis device may be supplied with electric power, not through the low-voltage secondary battery, but directly from a commercial power source.
Examples of an on-board device which is mounted on an electric vehicle and on which malfunction diagnosis should be made while the vehicle is not driven other than the evaporative emission control device include engine coolant cooling system and battery control device for batteries including secondary batteries. In any case, when diagnosis is made as to whether there is a malfunction in an on-board device, it is necessary to increase the accuracy of the malfunction diagnosis on the on-board device and prevent the amount of charge in an electric storage section which supplies electric power to the malfunction diagnosis device from becoming excessively low. The battery control device described in JP-A-2004-266937 may still be improved in this respect.